Friday, September 23, 2011

The Perlids (Common Stoneflies) in Our Streams


We've had clouds and rain all week -- with more rain on the way.  Ugh!  While I wait for the clouds to clear so I can get back to the streams, here's a quick look at the members of the "Common" stonefly family that, to date, I've found in local streams.  I'll note them by genus -- including the name of the species where I know it.

1.  Acroneuria abnormis -- pictured above.  This is the most common stonefly we see in our streams.
Widespread.

2. Acroneuria carolinensis.  To date, I have only found this species in the Rapidan River.  Abnormis and carolinensis differ primarily in the nature of the banding on the abdominal segments.


3. Agnetina.  I have only seen this genus in the Rivanna River.  Pictured is a small, immature nymph.  If I can find a larger one this fall, I will try to determine the species.


4. Paragnetina immarginata.  I have only seen this genus in the Rapidan River.


5. Neoperla.  I have only seen Neoperla in Powells Creek in Crozet.  Differs from all other "Commons" in having only two ocelli (not three).


6. Perlesta.  Fairly common, and found in both small streams and large rivers.  This seems to be the last Perlid to mature and hatch in the summer.  I saw them well into July, but I didn't see any anywhere until late May.


7. Eccoptura xanthenses.  This species seems to be confined to small streams, "tiny" streams.  I've seen them in Powells Creek, the Whippoorwill branch of the Mechums, and in two of the Moormans tribs that I explore.


That's it.  Of the genera keyed out and ID'd in Peckarsky's Freshwater Macroinvertebrates of Northeastern North America (p. 69), I have not yet found: Perlinella, Hansonoperla, Beloneuria, and Attaneuria.  The search goes on.

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All photos of these and other insects can be viewed at:

http://www.flickr.com/photos/aquaticinsects_of_central_virginia

Open the folder "live photos only".

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